Although recent advances have been made in lowering transition temperatures, existing superconducting materials exhibit superconducting properties only at temperatures substantially below normal environmental conditions. In spite of this fact, practical uses of superconducting materials in electric machines, such as electric motors, have been envisioned.
One example is the electric motor described in U.S. Pat. No. 4,577,126 to Malifert. The motor has superconductive field windings formed of cylindrical windings having an axis about the axis of rotation of the rotor. The rotor may be solid or in the form of a shaft on which are secured one or more disks. The armature windings alternate with and overlap rotor disks such that the internal windings are interleaved or are interfitted between the disks of the rotor. The windings may be formed on flat insulating supports in the form of disks which can be made of glass fiber reinforced resin.
U.S. Pat. No. 4,385,248 to Laskaris describes a support structure for a superconducting winding of a motor which minimizes frictional heat losses developed by relative sliding motion at the interface between the superconducting electrical winding and a support structure. A plurality of superconducting conductors are bunched together in close thermal and electrical contact with one another in a solid winding bundle. The winding bundle is then treated with epoxy resin so that all the individual conductors are epoxyed together.
U.S. Pat. No. 3,521,091 to Halas describes an electric motor having an isolated superconducting field coil constructed of foil strips which are damped by placing two strips in a side-by-side relationship and connecting the end of one strip to the beginning of the other. The armature is maintained at a cryogenic temperature above its superconductive transition temperature and is also of foil strip construction to improve cooling and resist centrifugal crushing and cut through.
Heretofore, practical applications of superconducting motors have been limited due to the requirement for maintaining temperatures substantially below the temperatures experienced in the vast majority of real applications.